Fermentation methods which are methods for substance production involving incubation of microorganisms or cells to be incubated can be roughly classified into: (1) a batch fermentation method and a fed-batch fermentation method; and (2) a continuous fermentation method.
In relation to the continuous fermentation method (2), a method has been proposed in which the microorganism or incubated cells are filtrated off with a separation membrane to recover a chemical from the filtrated liquid and, at the same time, the microorganism or incubated cells in the concentrated liquid are caused to be held in or are returned to the culture medium, thereby keeping the concentration of the microorganism or incubated cells in the culture medium high.
For example, a technique has been proposed in which continuous fermentation is performed in a continuous fermentation apparatus employing, as the separation membranes, flat sheet membranes made of an organic polymer (see Patent Document 1). Although the technique of Patent Document 1 is effective in continuous fermentation, the effective membrane area relative to the volume in which the flat-sheet membrane units have been installed is small. Consequently, production of a target chemical by this technique does not have a sufficient cost merit, and there has been room for investigation from the standpoint of heightening the efficiency.
In order to overcome the above-mentioned problem, a technique of continuous fermentation has been proposed in which hollow fiber membranes made of an organic polymer are used as separation membranes in a continuous fermentation apparatus (see Patent Document 2). In this technique, each membrane unit can have a large membrane area per unit volume and, hence, a remarkably heightened efficiency of fermentative production has been attained as compared with conventional continuous fermentation.
Known as a separation membrane module employing hollow fiber membranes is an integrated module which includes a cylindrical case and, housed therein, a bundle of a large number of hollow fiber membranes and in which both ends of the bundle of hollow fiber membranes have been fixed to the cylindrical case with an adhesive so that the end faces of the hollow fiber membranes in at least one end of the bundle are open. In fields where steam sterilization is necessary, such as the fermentation field, cartridge type modules in which cartridges are used in the state of having been disposed in cylindrical cases are frequently used in order to reduce the cost of modules. With respect to configurations of cartridge type hollow-fiber membrane modules, a module has been proposed in which one-side ends of hollow fiber membranes are held in a cylindrical case and the other-side ends are not held in the cylindrical case (see Patent Document 3).